Performance evaluation of nonsynchronized initial random access for mobile broadband systems

In this paper, a comparative analysis of the performance of the nonsynchronized initial random access channel in Mobile WiMAX and E-UTRA systems under different conditions (fast fading, multiuser interference) is carried out. The analysis is focused on the correlation properties of the code sequences used in each case. We evaluate their ability to provide low values for false alarm and erroneous detection probabilities (detecting a sequence that has not been transmitted) at the same time as guaranteeing low nondetection probabilities of the effectively transmitted sequences. Results show the promising performance of the E-UTRA scheme, even in high mobility scenarios, where the Doppler effect requires additional considerations to guarantee the correct system operation.     

Estimation of water diffusivity parameters on grape dynamic drying

A computer program was developed, aiming at estimating water diffusivity parameters in a dynamic drying process with grapes, assessing the predictability of corresponding non-isothermal drying curves. It numerically solves Fick’s second law for a sphere, by explicit finite differences, in a shrinking system, with anisotropic properties and changing boundary conditions.     

A neural network-based preset generation tool for a steel tandem cold mill

This paper traces the development of a software tool, based on a combination of artificial neural networks (ANN) and a few process equations, aiming to serve as a backup operation instrument in the reference generation for real-time controllers of a steel tandem cold mill. By emulating the mathematical model responsible for generating presets under normal operational conditions, the system works as an option to maintain plant operation in the event of a failure in the processing unit that executes the mathematical model. The system, built from the production data collected over six years of plant operation, steered to the replacement of the former backup operation mode (based on a lookup table), which degraded both product quality and plant productivity. The study showed that ANN are appropriated tools for the intended purpose and that by this instrument it is possible to achieve nearly the totality of the presets needed by this kind of process. The text characterizes the problem, relates the investigated options to solve it, justifies the choice of the ANN approach, describes the methodology and system implementation and, finally, shows and discusses the attained results.     

Study of the synergic effect of sulphate pre-treatment and platinisation on the highly improved photocatalytic activity of TiO2

An important improvement of the photocatalytic activity of sol–gel prepared TiO₂ has been achieved by sulphate pre-treatment, calcination at high temperature and further platinisation of the samples.

The presence of sulphuric acid clearly stabilised TiO₂ surface area against sintering, maintaining at the same time anatase phase until higher calcination temperatures than in non-sulphated samples. Platinisation of the samples with different nominal amounts of platinum (from 0.5 to 2.5 wt%) was performed and the influence of sulphate treatment on the dispersion and deposit size of platinum on the TiO₂ surface was studied.

Characterisation results and photocatalytic activity of these catalysts were compared with those of unmodified TiO₂. Simultaneously sulphated and platinised TiO₂ samples were highly active for phenol degradation, used as model reaction for the photocatalytic studies, having higher activities than only platinised or only sulphated samples. The activity of these samples were several orders of magnitude higher than that of the commercial TiO₂ Degussa P25 (platinised or unmodified) as well, with independence of the nominal amount of platinum of the samples.

A wide characterisation of the samples was performed and correlations between characterisation results and activity properties are reported.     

Synthesis and Characterization of Aurivillius Phases in the Bi–Ag–Ti–O System

New Aurivillius phases in the Bi–Ag–Ti–O system were investigated by means of a solid-state reaction and X-ray diffraction. We found that the oxygen partial pressure has a significant influence on the synthesis of the Aurivillius phases. The mixed-layer Aurivillius phase Ag_0.5Bi_8.5Ti₇O₂₇ was observed after firing in an O₂ flow, but a single-phase material is difficult to obtain. A single-phase compound of the four-layer Aurivillius phase Ag_0.5Bi_4.5Ti₄O₁₅ was obtained on firing in an oxygen partial pressure of 10 bar (1 × 10⁶ Pa). The dielectric properties (at 1 MHz) of the Ag_0.5Bi_4.5Ti₄O₁₅ compound were as follows: T _max=687°C, ɛ _r =166 (∼20°C), and tan δ=0.004 (∼20°C).     

Synthesis of cationic flocculants by the inverse microemulsion copolymerization of acrylamide with 60% 2‐acryloxyethyltrimethyl ammonium chloride in the monomer feed. II. Influence of the formulation composition,hydrophilic‐lipophilic balance,starting polymerization temperature,and reaction time

Acrylamide/2‐acryloxyethyltrimethylammonium chloride copolymers in inverse microemulsions, with 60% 2‐acryloxyethyltrimethyl ammonium chloride in the monomer feed and a concentration of active matter of 30% (w/w) as flocculants, were obtained by inverse microemulsion copolymerization. Inverse microemulsion formulations of comonomers, interesting from both technical and economical viewpoints, were polymerized by semicontinuous free‐radical copolymerization with sodium disulfite as the initiator. The influence of the formulation composition, hydrophilic‐lipophilic balance (HLB), starting polymerization temperature, and reaction time on the polymerization and final properties of the products as flocculants was studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:186–197, 2007